0s and 1s for Processors (CPUs)
06/13/2001
The Basics
Looking at the possibilities allowed by a number of digital signal lines provided to our device, with
- 4 signal-lines we would have 16 (24) possibilities,
- 8 signal-lines would allow 256 (28) possibilities,
- 16 signal-lines would allow 65,536 (216) possibilities.
These signal-line possibilities are useable for either CPU instruction selections, or for memory address selections.
Example #1
4 signal-lines would allow 16 possible instructions, for a very simple CPU, or 16 possible memory address locations.
If those signal-lines were accessed a second or third time, it would allow more possibilities.
Example #2
Those same 4 signal-lines could be accessed twice, with the first access defining one of 16 possible groups of instructions, each of which could define one of 16 possible instructions within this group, for a possibility of 256 total possible instructions.
Example #3
8 signal-lines would allow 256 possible instruction selections at once, without having to do 2 accesses.
Example #4
Those same 8 signal-lines could be accessed twice, with the first access defining one of 256 possible groups of instructions, each of which could define on of 256 possible instructions within this group, for a possibility of 65,536 possible instructions.
If there are enough lines available, those lines could be subdivided into groups for multiple purposes.
Example #5
8 signal-lines would allow 256 possible instruction selections, on the first pass, and a second access of those 8 signal-lines would allow (in the case of data) 256 locations to retrieve or store data.
Example #6
8 signal-lines would allow 256 possible instruction selections, on the first pass, and a second and third access of those 8 signal-lines would allow (in the case of data) 65,536 address locations to retrieve or store data.
Example #7
16 signal-lines would allow the first 8 signal-lines to be used for instruction decode, and the second set of 8 signal-lines to be used for memory-access selection of 256 possible locations, on one pass!
Example #8
16 signal-lines would allow anything from 256 to 65,536 instruction selections on the first pass, with a second pass to allow (in the case of data) selection of 65,536 address locations to retrieve or store data.